to begin with...much of the confusion comes from misconceptions about the timing and duration of the passover or feast of unleavened bread... many are under the mistaken impression that passover and the feast of unleavened bread are two separate festivals...with the feast of unleavened bread beginning twenty-four hours after the passover seder...
but scripture indicates that this idea is incorrect...and shows that the terms 'passover' and 'feast of unleavened bread' are actually interchangeable names for the same seven day feast...
ezekiel 45:21..."In the first month, on the fourteenth day of the month, you shall have the Passover, a feast of seven days; unleavened bread shall be eaten."
luke 22:1..."Now the Feast of Unleavened Bread, which is called the Passover, was approaching."
furthermore scripture shows that the passover seder marked the first day of the feast unleavened bread...
matthew 26:17..."Now on the first day of Unleavened Bread the disciples came to Jesus and asked, 'Where do You want us to prepare for You to eat the Passover?'"
mark 14:12..."On the first day of Unleavened Bread, when the Passover lamb was being sacrificed, His disciples *said to Him, 'Where do You want us to go and prepare for You to eat the Passover?'"
luke 22:7..."Then came the first day of Unleavened Bread on which the Passover lamb had to be sacrificed."
so the passover seder corresponded with the first day of the feast of unleavened bread...the feast of unleaved bread did -not- begin a day later as many people have assumed...
the feast of unleavened bread began on a fixed date in the hebrew calendar each year...specifically the fifteenth day of the month of abib...
leviticus 23:6..."Then on the fifteenth day of the same month there is the Feast of Unleavened Bread to the Lord; for seven days you shall eat unleavened bread."
numbers 28:17..."On the fifteenth day of this month shall be a feast, unleavened bread shall be eaten for seven days."
so the passover and feast of unleavened bread went as follows...
abib 15...first day of the feast of unleavened bread...beginning with passover seder...sacred assembly held...
abib 16...second day of the feast of unleavened bread...
abib 17...third day of the feast...
abib 18...fourth day...
abib 19...fifth day...
abib 20...sixth day...
abib 21...seventh day of the feast of unleavened bread...sacred assembly held...
someone will probably object that scripture states that the passover seder was held on the evening of the -fourteenth- day...implying that it was the fourteenth day when the seder was held...with the feast of unleavened bread not beginning until one day later on the fifteenth day...
but this notion is based on another misconception...it turns out that when scripture speaks of the evening of a certain day...it is actually indicating the -end- of that day and the -beginning- of the next day... this convention is clear from the scripture on the day of atonement...
leviticus 23:27-32..."On exactly the tenth day of this seventh month is the day of atonement; it shall be a holy convocation for you, and you shall humble your souls and present an offering by fire to the Lord. You shall not do any work on this same day, for it is a day of atonement, to make atonement on your behalf before the Lord your God. If there is any person who will not humble himself on this same day, he shall be cut off from his people. As for any person who does any work on this same day, that person I will destroy from among his people. You shall do no work at all. It is to be a perpetual statute throughout your generations in all your dwelling places. It is to be a sabbath of complete rest to you, and you shall humble your souls; on the ninth of the month at evening, from evening until evening you shall keep your sabbath."
it is clear from this scripture that the evening of the ninth day was regarded as the -ending- of the ninth day and the -beginning- of the tenth day which was the day of atonement...with the ninth day not actually being part of the day of atonement...
so applying scripture's own convention to passover and the feast of unleavened bread...it is equally clear that the evening of the passover seder was the -end- of the fourteenth day of the month and the -beginning- of the fifteenth day of the month...the fourteenth day itself was not part of the passover observance or the feast of unleavened bread...
having established that...we can say that anything that took place in the daylight hours immediately following the night of the seder happened on what scripture would call the fifteenth day...
that is significant because jesus was crucified in the daylight hours immediately following the night of the seder he held with his disciples...that means jesus was crucified on the fifteenth day of the month...
someone may try to argue that jesus' last supper was not actually the passover seder...but that is disproved by mark 14:12...which i quoted above...it clearly shows that the passover lambs were killed on the evening of the same day jesus' disciples obtained the use of the upper room for his last supper...so there is no doubt that the last supper was a passover seder...
having established that jesus was crucified on the fifteenth day of the month of abib...we now look to the fact that the day following jesus' crucifixion was a sabbath...
mark 15:42..."When evening had already come, because it was the preparation day, that is, the day before the Sabbath,"
john 19:31..."Then the Jews, because it was the day of preparation, so that the bodies would not remain on the cross on the Sabbath (for that Sabbath was a high day), asked Pilate that their legs might be broken, and that they might be taken away."
the entire basis of all 'anti good friday' arguments is the notion that this sabbath could have been one of the days of assembly associated with the feast of unleavened bread...however we can now see that this is impossible...
given that jesus was crucified on the fifteenth day of abib...it is clear that the sabbath of the following day would have fallen on the sixteenth day of abib...however in the laws regarding the passover and feast of unleavened bread there is no provision for a sabbath on the sixteenth day of abib...but only on the fifteenth and twenty-first days of the month...
in fact it is apparent that the sabbatical assembly was actually held on the day of the crucifixion...which likely explains how the jews were so quickly assembled before pilate to observe the trial of jesus...they would have been assembling anyway...
this all means that this sabbath can -only- be the weekly saturday sabbath...and if the day after jesus' crucifixion was a saturday...then jesus was crucified on a friday...